Facts About Fluoridation

Water fluoridation is the addition of the chemical fluoride to public water supplies, for the purpose of reducing cavities.

Currently, two-thirds of Americans have fluoridated public water, according to the Centers for Disease Control and Prevention (CDC). Of those served by municipal water systems, the figure climbs to 73.9 percent.

What is fluoridation?

About 90 percent of the fluoride added to public water supplies comes from silicofluorides, chemicals produced mainly as byproducts from the manufacture of phosphate fertilizers, according to the CDC.

Fluoride is added to public water supplies at an average concentration of about 1 part per million (1 ppm), or slightly below. Naturally occurring fluoride concentrations in surface waters depend on location but are generally low and usually do not exceed 0.3 ppm. Groundwater can contain much higher levels, however.

How fluoridation works

Fluoride works by binding to tooth enamel, which is primarily made up of hydroxylapatite, a crystal composed of calcium, phosphorus, hydrogen and oxygen, according to Scientific American. By replacing the hydroxyl molecule on hydroxylapatite, fluoride makes the tooth more resistant to acid attack from bacteria. Exactly how fluoride helps protect teeth, and how much it protects them, however, isn't completely clear.

Tooth decay, when left untreated, can lead to serious health problems, such as infections that can spread into the jaw. Tooth decay has declined in the United States since fluoridation began; however, it has also declined in other countries that do not fluoridate.

Fluoridation controversy

Since its introduction beginning in the 1940s, fluoridation has been the source of considerable controversy. Pro-fluoridation supporters say that the process is "safe and effective" for reducing cavities, particularly in poor children. Water fluoridation is endorsed by the American Medical Association, the American Dental Association and the CDC, which lists it as one of the top 10 most important public health measures of the 20th century.

Those on the opposite side say that it is unethical form of mass-medication, without each individual's consent or knowledge. By putting fluoride in drinking water, the dosage cannot be controlled, since some people — like laborers and people with kidney problems — drink much more water than others. Fluoride opponents cite studies showing that low levels of fluoride have been linked to a number of negative health effects like bone fractures, thyroid disorders and impaired brain development and function.

The most obvious health effect of excess fluoride exposure is dental fluorosis, which when mild includes white streaks, and when severe can include brown stains, pits and broken enamel. As of 2010, 41 percent of kids ages 12 to 15 had some form of dental fluorosis, according to the CDC.

Within the last 15 years, research has revealed that fluoride primarily works topically, such as when it applied to the teeth in fluoride-rich toothpaste. People opposed to fluoridation have argued out that since this is true, it needn't be added to water. Today people are exposed to many more sources of fluoride than when it was first introduced in the 1940s — the first fluoridated toothpaste, Crest, wasn't introduced until 1955.

Is fluoride bad for you?

It depends who you ask; fluoride is unquestionably toxic at certain concentrations. The CDC says that the level at which it is added to the water (around 1 ppm) is safe and effective.

The most comprehensive report on fluoride was published in 2006 by the National Research Council, done at the behest of the Environmental Protection Agency. That group found that the upper limit for fluoride, at 4 ppm, was too high to prevent a certain percentage of kids from developing severe dental fluorosis and recommended the EPA lower this limit. The agency has yet to change this limit.

Water is fluoridated in 29 of the 30 largest cities. The exception is Portland, Ore. For the fourth time since 1956, voters in Portland defeated a plan on May 21 to add fluoride to the public water supply. For weeks, residents had been contentiously debating fluoridation.

One study published in the fall of 2012 in the journal Environmental Health Perspectives found a link between high fluoride levels found naturally in drinking water in China and elsewhere in the world, and lower IQs in children. The paper looked at the results of 27 different studies, 26 of which found a link between high-fluoride drinking water and lower IQ. The average IQ difference between high and low fluoride areas was 7 points, the study found.

Douglas Main

Douglas has written for the New York Times Green Blog, Popular Mechanics and Discover Magazine. He has an M.A. in journalism from the Science, Health & Environmental Reporting Program at New York University. Before that he studied biology and English literature at Washington University in St. Louis.